KEY POINTS:
More than 3000 New Zealanders are dropping off the blood donor books annually, leaving the country just five years away from a blood shortage crisis.
New Zealand Blood Service marketing manager Paul Hayes said the trend had been developing for four years.
Supply was keeping up with demand, but more elective operations - enabled by increased health spending - and an ageing baby-boomer population whose health concerns were expected to increase painted a gloomy picture, he said.
If the trend was not halted, New Zealand could be five years away from severe blood shortages.
That could force many elective surgery operations to be cancelled and blood might be available only on a day-by-day basis, he said.
Winter would be the worst-affected period, as the medication required for some cold-weather-related illnesses made many donors ineligible to give blood.
Today is World Blood Donor Day - which Mr Hayes hoped new donors would mark by coming forward, and old donors by getting themselves back on to the donor books.
Such a move was all that would avert the crisis.
Each donor gives on average nearly a litre of blood a year.
New donors were signing up each year, but the net loss since 2004 had shrunk the donor list from 105,000 to 93,000.
Of those still giving blood, the large majority were older than 45, Mr Hayes said.
As they got older, their health concerns often increased, forcing them off the list.
While there were a large number of donors younger than 21, the group in the middle was very small, he said.
"It's absolutely a generational thing," Mr Hayes said.
"I'm not so sure that, as a people, we're as giving to the country as we were in the past. And New Zealanders are a very mobile people these days."
That mobility meant donors often forgot to keep the Blood Service updated on their contact details, he said.
But as people got older, they became more settled and began to see friends and family requiring blood and blood products.
Some people also held concerns that their donated blood would most likely be used to assist drunk drivers who had been involved in car accidents, he said.
But accidents of all types accounted for only 7 per cent of blood demand.
Cancer patients required the largest share, 27 per cent, because radiotherapy and chemotherapy knocked out the bone marrow responsible for making blood, he said.
Fears of becoming infected through giving blood were also misguided, he said.
A new set of equipment was used for each donation, then discarded.
The donation of 470ml was about 7 or 8 per cent of the average donor's total blood, but all except those with the most active jobs were capable of going straight back to work after giving blood.
The donated blood volume was replaced within 24 hours of the donation, and the total red blood cells were replenished within two weeks.
The Blood Service spends about $80 million each year, which is recouped from district health boards.
